This invention relates generally to nuclear steam generators and more particularly to a modular sludge collecting system for collecting concentrated solids from recirculating water and feedwater within the generator.
It is well known in the art of nuclear steam generators to have certain spaces or volumes therein of relatively low velocity fluid flow to give the solids suspended in the fluid an opportunity to settle out in an area where they can be relatively easily collected and eliminated from the generator.
One example of such structure in a shell and tube type vapor or steam generator is shown in U.S. Pat. No. 3,916,844, wherein the feedwater, upon entering the shell, is received in a large annular settling chamber of low liquid velocity which extends adjacent to the generator shell. This settling chamber intercepts the incoming feedwater, which does not have a very high concentration of suspended solids per unit volume, and also receives returning carry-over water which has a much higher concentration of suspended particles, but which becomes considerably diluted upon mixing with the incoming feedwater within the chamber. Consequently, to be effective, a very large volume of low velocity feedwater is necessary for effective removal of suspended solids.
U.S. Pat. No. 4,303,043 discloses a nuclear steam generator having a settling chamber or sludge collection chamber which is interposed between the recirculating carry-over water and the incoming feedwater, to intercept the recirculating water and retain at least a portion thereof in a sustantially stagnant condition to permit the entrained solids to be deposited within the chamber. Baffle means are provided to limit the exchange of the continuously incoming carry-over water with the water already retained in the chamber to minimize turbulence, yet permit some rate of exchange between the incoming recirculating water and the water in the chamber from which the sediments have already been removed. Although the large settling chamber disclosed in that patent is suitable for original equipment fabrication, that system cannot be feasibly applied on a retrofit basis because of internal component obstructions and because of limited access to the upper regions of the steam generator. In both of the above patents, sludge removal is effected through a single blowdown pipe, which if clogged, would disable the entire sludge collecting system.